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5667Re: creating a cosmacelf simulator in C

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  • ted_rossin
    Oct 3, 2008
      I just uploaded the source code to my Elf emulator in the
      Files/Simulators folder (TedsElf.zip). It is in C++ but should give
      you some hints on how to proceed. The source is for a Visual Studio
      project. The real meat is in 1802.cpp and 1802.h. You can find
      programs that will run and instuctions on my web site:


      One problem with many of the 1802 emulators that I tried is that
      they are not coded up for real-time operation. They tend to run as
      fast as they can which tends to be much faster than the real machine
      and varies based on processor speed. I use Windows timers to step
      my emulator at a periodic rate (I think every 50ms) for a tunable
      number of steps. This keeps the simulator speed constant across
      multiple machines. I don't have it perfectly tuned up but it does
      run within 10% of my real Elf system.

      The point I'm trying to make is to not make your emulator a giant
      while loop but instead write it such that it is a subroutine that
      maintains the state of the machine so that it can be called once per
      unit of activity. For example, you could model all the machine
      states and call the subroutine once per clock cycle. I choose to do
      it once per instruction but I maintain state as to the number of
      machine cycles executed (2 or 3 per instruction). Machine cycles
      are 8 clock cycles.

      This also allows you to hook up devices to your emulator such as
      LEDs, keyboards or 1861 video chips.

      Good luck and have fun. I enjoyed the process and am now able to
      develope code for my 1.6 MHz Elf on a 3.0 GHz PC.

      --- In cosmacelf@yahoogroups.com, akshay parelkar <va7aax@...> wrote:
      > Hi Fans of Cosmac Elfs,
      > I recently discovered this fancy little computer while searchig on
      the web. I dont have a Real Cosmac Elf yet(Have digital ones
      > Lately, I have been thinking about writing up my own code (in C)
      to simulate the Cosmac elf. I dont expect this project to compete
      with the ones already available, just something with which I can
      undertand more about the 1802 itself and improve and exercise my own
      (rather limited) knowledge of C.
      > Can somebody give some suggestions as to how and where I
      can/should start?
      > Also, another idea rolling in my mind is, Would it be possible to
      build a replica Cosmac Elf based on a PIC or has anyone already done
      > Thanks,
      > Long live cosmac elfs! 
      > [Non-text portions of this message have been removed]
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